MeBr is a soil fumigant that has been extensively used throughout the world for the elimination of pests (e.g., nematodes, fungi) during the cultivation of a wide variety of vegetables, specialty fruit (i.e., strawberries) and flowers. Typically, MeBr is added to soils in conjunction with chloropicrin ("tear gas") to enhance toxicity and to serve as a warning agent. A tarp is used to cover the area to which the MeBr is applied.
Because MeBr has a relatively long tropospheric residence time (currently the subject of scientific debate but generally accepted to be between 0.7 and 1.8 years), some portion of the atmospheric burden will be transported up to the stratosphere and participate in a series of reactions which result in the destruction of the Earth's protective ozone layer. Because molecules of bromine are about 50-fold more efficient at destroying ozone than molecules of chlorine, MeBr has become a focus of an addenda to the Montreal Protocol of 1991, which calls for an international phasing out of the use of MeBr over the next fifteen years. It is noted that natural sources of MeBr account for most of the emissions to the atmosphere, while agricultural fumigations appears to account for 16-33%. Nonetheless, this phase-out of MeBr, which will be accelerated in the United States due to implementation of the Clear Air Act (2001), will deprive food growers of a very useful, non-residue accumulating pesticide.
Methods for combating the problems associated with using MeBr as a fumigant include physical manipulations, such as soil compaction and deeper injection of MeBr, with the purpose of increasing the retention of MeBr within the soil, thereby providing more extensive degradation and a subsequent decrease in the outward flux thereof to the atmosphere. In addition, the use of thicker, impermeable covering tarps has been proposed to reduce MeBr losses to the atmosphere. Another approach is to use methyl iodide rather than MeBr because of the very short atmospheric residence time thereof, and reference is made in this regard to U.S. Pat. No. 5,518,692 to Grech et al. for a discussion of this approach as well as the general problem under consideration. Methyl iodide has different physical properties from MeBr and may not be as effective in destroying crop pests, and, in any event, is substantially more expensive. Reference is also made to U.S. Pat. No. 4,664,805 to Focht which relates to a method for accelerating the decontamination of an environment contaminated with toxic halogenated organic compounds (MeBr is one of very many examples) by adding both (1) microorganisms which are not indigenous to the environment and (2) a non-toxic analog of the halogenated organic compound.
A clear need exists for a way to use MeBr in the fumigation of fields which would satisfy the different needs and requirements of growers, fumigators, environmentalists and various world and U.S. Agencies and local governments and, more particularly, for a method or way of applying MeBr in fumigating fields so that the MeBr can function to eliminate crop pests, but would not emitted to the atmosphere over the periods of tarping operations (about 6 days).